Mini Mill Z axis #3

This is my third and final Z axis. Based on a comment on my original Z axis, this drives the "precision" worm screw. If you didn't snort milk through your nose when reading the scare-quotes, the precision drive is anything but precision - mine had about 0.040" slop. However being the Z axis you can leverage this wonderful thing called "gravity" so as long as you have positive down-force (gravity, air cylinder, can't it be both?) then you can (almost) guarantee the same side of the screw will be